SQL for Duplicate Registrations | Dataford Interview Questions

Write a query to identify duplicate student registration records based on name and birthdate, keeping only the earliest registration.

Return only duplicate groups, retaining the earliest record in each group. Treat NULL values as belonging to the same matching group.

Output

One row per duplicate name and birthdate group
Columns: student_name, birth_date, registration_id, registered_at, and duplicate_count
Include the earliest registration and the total number of records in its group
Order by student_name, birth_date, registered_at, and registration_id, with NULL names and birthdates last

student_registrations

Column	Type	Description
registration_idPK	INT	Unique registration record identifier
student_name	VARCHAR(150)	Student's full name
birth_date	DATE	Student's date of birth
registered_at	TIMESTAMP	Timestamp when the registration was created

Your question is SQL for Duplicate Registrations. Start with the requirements and the one table in the Question tab.

Run and submit as often as you like. When you're ready, talk me through your approach or go straight to the code.

Write a query to identify duplicate student registration records based on name and birthdate, keeping only the earliest registration.

Return only duplicate groups, retaining the earliest record in each group. Treat NULL values as belonging to the same matching group.

One row per duplicate name and birthdate group
Columns: student_name, birth_date, registration_id, registered_at, and duplicate_count
Include the earliest registration and the total number of records in its group
Order by student_name, birth_date, registered_at, and registration_id, with NULL names and birthdates last

student_registrations

Column	Type	Description
registration_idPK	INT	Unique registration record identifier
student_name	VARCHAR(150)	Student's full name
birth_date	DATE	Student's date of birth
registered_at	TIMESTAMP	Timestamp when the registration was created

Your question is SQL for Duplicate Registrations. Start with the requirements and the one table in the Question tab.

Run and submit as often as you like. When you're ready, talk me through your approach or go straight to the code.